In a known boring rod extension of this type (see DT-OS 1752 014) the boring tool carriers project freely above the two ends of the housing.
They are thus, in particular when they are adjusted to their outermost position by means of the adjusting bushing, not strong enough to be able to carry out coarser work with known tools, that is rough work with greater removal of swarf. In addition, with the known tool the boring tool carrier is mounted in bearings to be unable to rotate within the chuck socket and the chuck socket is mounted so as to be unable to rotate within the housing, for which purpose it is necessary, in each case, to provide grooves and pins, which increases the manufacturing costs.
The basic object of the invention is therefore to design an extension for a boring rod, of the type described in the introduction, such that the boring tool carriers are better supported and the extension also has a simpler construction.
This is achieved according to the invention in that the housing has a projection with, in each case, a plane supporting surface on the side turned away from the boring tool, on which said supporting surface there is supported a part of the boring tool carrier which is broadened out relative to the cylindrical shaft by means of a similar supporting surface. Since the projection is rigidly joined to the housing, that is it forms a single unit with it, the boring tool carrier is securely supported even when it is in its outermost position. Because of the marked increase in strength thus produced, not only is coarser work with a greater removal of swarf possible; but the accuracy of performance of the tool in fine turning is increased. At the same time the plane supporting faces prevent rotation of the boring tool carrier relative to the housing, so that guide pins and grooves on the boring tool carrier, previously used to prevent such rotation, are no longer necessary. In addition, the plane surface of application offers an effective protection against rotation due to the markedly higher forces produced during coarser working.
The projection conveniently extends, on the side turned away from the boring tool up to about the level of the axis of the boring tool carrier. In this way it is also possible to achieve support of the boring tool carrier in the axial direction of the boring rod, that is in the direction of feed.
Further, the broadened out part of the boring tool carrier advantageously has substantially the same breadth as the housing and its projection, so that the boring tool projects somewhat beyond the housing in the axial direction of the boring rod. Because of this, it is also possible to work blind holes and collar fittings within a bore. In addition, it is possible with this design to employ a substantially larger interchangeable and rotatable cutting plate as the boring tool. The above-mentioned increased strength of the whole tool is thus also to be taken into account in the sense that it is possible to undertake a larger removal of swarf with larger cutting plates.